Electrical circuit—Amplifies sound

Overview

Microphone amplifier

Coupling condenser

Dual-shaft, quad-unit volume

Line amplifier

Sound picked up by the microphones is amplified in the analog circuit, which achieves a frequency response that reaches the high frequencies (Figure 2) and enables the wide dynamic range of PCM-D1.

The microphone amplifier provided for each channel is Analog Devices’ AD797, which boasts ultra-low noise and distortion.

A variable gain circuit is adopted for amplitude control, thus improving the actual signal-to-noise ratio.

In the signal line, direct current is removed by Elna’s coupling condenser, which has a separator made of synthetic mica mix paper.

Figure 2: Electrical circuit, frequency response

Adual-shaft, quad-unit volume control with ten times the life of a standard volume control was developed for recording. Special carbon ink is applied to the resistor in the control to suppress noise produced by sliding.

Like the microphone amplifier, the line amplifier, AD8672, is provided by Analog Devices.

Interference between blocks is prevented by placing the analog circuit on a different board from digital circuits and providing separate ± power. The analog circuit also achieves superior linearity so that the recorded sound is output faithfully (Figure 3).

Figure 3: Electrical circuit, linearity

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